(a) Field of the Invention
The present invention relates to a display device and a driving method thereof and in particular, a touch detectable display device and a driving method thereof.
(b) Description of Related Art
A liquid crystal display (LCD) includes a pair of panels provided with pixel electrodes and a common electrode and a liquid crystal layer with dielectric anisotropy interposed between the panels. The pixel electrodes are arranged in a matrix and connected to switching elements such as thin film transistors (TFTs) such that they receive image data voltages row by row. The common electrode covers entire surface of one of the two panels and it is supplied with a common voltage. A pixel electrode and corresponding portions of the common electrode, and corresponding portions of the liquid crystal layer form a liquid crystal capacitor that as well as a switching element connected thereto is a basic element of a pixel.
An LCD generates electric fields by applying voltages to pixel electrodes and a common electrode and varies the strength of the electric fields to adjust the transmittance of light passing through a liquid crystal layer, thereby displaying images.
Recently, an LCD incorporating photosensors has been developed. The photosensors senses the change of incident light caused by a touch of a finger or a stylus and provides electrical signals corresponding thereto for the LCD. The LCD determines whether and where a touch exists based on the electrical signals. The LCD sends the information on the touch to an external device that may return image signals to the LCD, which are generated based on the information. Although the photosensors may be provided on an external device such as a touch screen panel to be attached to the LCD, it may increase the thickness and the weight of the LCD and it may make it difficult to represent minute characters or pictures.
A photosensor incorporated into an LCD may be implemented as a thin film transistor (TFT) disposed in a pixel displaying an image. However, such a photosensor generates an output that varies depending on a circumference such as the intensity of an external light or of a backlight lamp, and thus there is an area where a touch may not be easily detected. This area is referred to as a dead zone and a photosensor in the dead zone generates an output having levels that may not be easily distinguished with and without a touch.